In certain gas sensor applications, it is desirable to keep the sensor isolated from the external environment without impeding its functionality. Such isolation can be for the purpose of reducing or minimizing heat loss, reducing or minimizing the amount of light reaching the sensor, and/or reducing or minimizing the consequences of mechanical intrusion. Often, a sensor is operated at a given temperature, typically greater than that of the surrounding gas stream it is sensing. This is sometimes accomplished by the use of heat-producing devices disposed on the same substrate as the sensor. When this is the case, there is a finite amount of heat lost to the gas stream surrounding the sensor, as well as to the components and structures in thermal (and electrical) contact with the sensor. This heat loss is proportional to magnitude of power loss from the entire system in which the sensor has been incorporated. It is therefore desirable to reduce or minimize such heat loss from the sensor.
Conventional, prior art thermal isolation techniques include fabricating the sensor itself in such a way as to create structures to provide thermal isolation (see, for example, U.S. Pat. Nos. 5,211,053, 5,464,966, 5,659,127, 5,883,009 and 6,202,467). Such exemplary thermal isolation techniques were designed specifically for the type of construction of the sensor involved and did not overcome the problems associated with heat loss at an assembly level, that is, where the sensor is configured as part of a greater assembly. Prior implementations of such gas-sensing devices, such as catalytically-based gas sensors, have employed different techniques to thermally isolate the device, such as suspending the device, within the gas stream being sensed, using individual wires that electrically connect the sensing device to its downstream processing and control circuitry (see, for example, U.S. Pat. No. 5,902,556), but these methods are not preferred for a sensor with multiple connections.
Suspending a sensor by, for example, three to six individual wires to thermally isolate the sensor is problematic in configurations involving multiple sensor elements. In particular, multi-element sensor configurations have a large number of leads associated with the sensor, making it difficult to achieve an adequate degree of thermal isolation, in the volume provided, because the greater number of leads tends to conduct significant amounts of heat away from the sensor. Fabricating such a suspended assembly is prohibitively costly and overly complex.
Prior art gas sensor configurations with multi-element sensors mounted on a ceramic base or suspended by leads have been unable to achieve an adequate degree of thermal isolation such that the power requirements of the gas sensor configuration can be significantly reduced. Such prior art configurations typically involved bonding the sensor to a ceramic element, sometimes referred to “dual in-line package” in which two rows of pin connectors extend from a ceramic substrate. The pin connectors of the dual in-line package align with and are insertable into mounting holes in standard circuit boards. Prior art gas sensor configurations therefore exhibit undesirably high thermal losses and require greater amounts of power to compensate for such thermal losses.